Maps and Map Projections How Maps Can Mislead Us
A Globe Is the only truly accurate representation of the earth
A flat surface It is easy to portray a flat surface on a flat piece of paper
But there is no way to accurately portray a 3-dimensional round surface on a flat piece of paper Therefore all maps are distorted
Distortion will occur in at least one of these map components: Size (area) Shape Distance Direction
Making Maps Mapmakers have devised many different methods for making maps of the world
Projections The different methods are called projections The term projection refers to projecting the 3-dimensional globe onto a flat surface
Equivalent A map that is equivalent is accurate in size or area It is NOT going to be accurate in shape
Peter s map is equivalent
Conformal A map that is conformal is accurate in shape It will NOT be accurate in size (area)
Mercator map is conformal
A world map cannot be both equivalent and conformal Equivalence and conformality are mutually exclusive properties
Common Map Projections Cylindrical Conical Planar or polar Compromise
Tangency Each projection is accurate at the point(s) of tangency only Cylindrical: equator (line) Conic: mid latitude (line) Planar: one pole only (point) Further away from point(s) of tangency = more distortion
Cylindrical
Cylindrical Projections Common for world maps Distorts size (area) more in areas farthest away from the equator Distortion greatest in northern latitudes most of the northern hemisphere s land mass is far from the equator Mercator is the most common cylindrical projection
Conical
Conical Projections Best for continents in mid latitudes North America Europe Russia Not useful for a world map Unless several are put together
Planar or Polar (Azimuth)
Polar Projections Only one hemisphere Arctic Ocean in the northern hemisphere Antarctica in the southern hemisphere Not good for mid latitudes, low latitudes don t show at all
Compromise Projections Minimize distortion in one aspect AND Keep the most accuracy in other aspects Mollewide Robinson Goode s Homolosine (interrupted)
Robinson Mercator Distortion Compared Mollewide
Scale All maps have a scale Scale relates map size to actual earth size A scale of 1:10,000 means that one unit of measurement on the map will equal tenthousand of the same units on the surface of the earth
Legend The legend is the key to reading the map Defines the colors and symbols Map scale will be in the legend or at the bottom of the map Ratio 1:10,000 Fractional 1/10,000 Words One inch equals ten-thousand inches Graphic looks like a ruler
Large Scale vs. Small Scale A large scale map portrays a small part of earth s surface City Campus Classroom
Cholera Map of London
City Map of Denver
A small scale map portrays a large portion of earth s surface World map the smallest scale of all 1:13,000,000 is the scale of our wall map
Scale and Distortion The smaller the scale of the map, the larger the portion of earth s surface is being shown The larger the portion of earth s surface, the more curvature The more curvature, the more distortion will occur in transposing it to a flat map
Extremely small scale maps, like world maps, have the most distortion Large scale maps, like a map of the college campus, have little or no distortion
Types of Maps Maps are generally made for a specific purpose
Road Map Roads, towns, cities, and other data useful for transportation Most familiar type of map to the average person But there are many other types of maps!
Political Show man-made divisions, such as the borders of states or countries
Political vs. Physical
Physical Show physical characteristics, like mountains, lakes, and rivers Often show elevation by color coding
Topographic Shows landforms and elevations in detail Contour lines - lines that connect places with equal value, in this case feet above sea level
Thematic These maps each have a special theme Physical Climate Ocean Currents Biomes Cultural Population Ethnicity Income
Map of World Population